Light emitting diodes are widely used in optical displays, traffic lights, data storage, communications, medical and many other applications.
The development of blue LEDs and laser diodes has attracted considerable research activity to the growth of group III-nitrides. The band gap of group III-nitrides can be varied to provide light over nearly the whole spectral range from near UV to red. Accordingly, group III-nitrides find use in active regions of these devices.
The growth of InxGa1−xN alloys and quantum wells is extremely difficult mostly due to the trade-off between the epilayer quality and the amount of InN incorporation into the alloy. Growth at high temperatures of approximately 800° C. typically results in high crystalline quality but the amount of InN in the solid is limited to low values because of the high volatility of indium. Lowering the growth temperature results in an increase in the indium content at the expense of reduced crystalline quality. The lattice mismatch and different thermal stability of the two constituents, InN and GaN, also complicate the growth of InxGa1-xN. The lattice mismatch can lead to a miscibility gap, which causes fluctuations of In content across the film. Singh and co-workers provided strong evidence of phase separation in InGaN thick films grown by molecular beam epitaxy (MBE). Other researchers reported phase separation in thick InGaN films grown by metalorganic chemical vapor deposition (MOCVD). Behbehani reported the co-existence of phase-separation and ordering in InxGa1−xN with x>0.25. Up to now, growth of InGaN/GaN quantum wells (QW) with emission in the green is still a challenging task.
InGaN is a very important material because it is used in the active layer of LEDs and laser diodes (LD), However, researchers have not reached consensus on the optical emission mechanism in InxGa1−xN/InyGa1−yN QWs. There are a few theories; one attributing emission to In-rich quantum dots (QDs), one attributing emission to the piezoelectric effect and another combining aspects of both. Indium-rich QDs can be formed by spinodal decomposition, Stranski-Krastanov (SK) growth mode, or using antisurfactants.